A joint replacement procedure is sometimes necessary to repair a joint having a diseased or damaged articular surface. Such a procedure may involve removal of the diseased or damaged portions of the joint and replacing them with a prosthetic implant. This is often a desirable procedure for ball-and-socket type joints, particularly the shoulder and hip joints. A shoulder joint replacement procedure, for example, often involves removal of the humeral head and replacement thereof with an implant including a stem and a head. It is important that the implant be positioned correctly within the joint in order to ensure that appropriate joint kinematics, including range of motion, are preserved so as to replicate, as closely as possible, those of the original joint.
The structure of prosthetic joint components has been developed to be suited for permanent implantation into the joint and includes features that may promote bony ingrowth, adhesion using cement, press-fit or a combination thereof. Particularly, in the case of implants including a stem, such as those used in shoulder arthroplasty, these features are generally included on the outside surface of the stem. Such features may not be well-suited for use during the assessment of joint kinematics. Accordingly, instruments such as trials have been developed to be used in this part of the procedure. Generally, trials are affixed to the bone during joint kinematic evaluation and removed therefrom after a proper position for the implant has been determined.
Typically, trials are designed to correspond to an implant in size and shape. In a shoulder arthroplasty procedure, for example, a trial may be designed to be temporarily inserted into a prepared medullary canal of the humerus in a manner similar to that of an implant. Known trials may take many forms. For example, an expanding trial stem, such as that described in U.S. Pat. No. 8,216,320, the entire contents of which are hereby incorporated by reference herein, includes a stem that may be expanded after insertion into the medullary canal. When using such trial stems, particularly in shoulder replacements, it may be difficult to establish the proper position and orientation for the implant in the humerus. It would thus be desirable to have guides that simplify the determination of proper positioning of the implant during use of a trial stem.